A direct anion exchange ion chromatography (IC)-based method for the detection of the chemical warfare (CW) agent degradation product, O-isopropyl methylphosphonic acid (IMPA) in agar medium has been developed. This is the first report of the development and validation of an IC-based method for the analysis of IMPA in a microorganism and agar matrix. In these experiments, IMPA served as a surrogate for the CW agent GB (Sarin) in a development program for living micro-organism-based CW agent destruction systems. Petri dishes containing the medium with 10, 100 and 1000 μg/mL IMPA were used. Samples were prepared by dilution of the agar medium with deionized water followed by sonication and then filtration before the analysis by IC/conductivity detection. Using this method, the amount of IMPA in the Petri dishes was measured. Excellent separation efficiency and freedom from interference due to common anions such as chloride and sulfate was obtained in the developed method. Retention time precision was ⩽1.0% relative standard deviation (%RSD) and the detection limit was 0.1 μg/mL. Calibration curves using five IMPA concentrations over the range 1-100 μg/mL in blank agar matrices at three different dilutions (0-fold, 4-fold, and 40-fold diluted with reagent water) gave correlation coefficients (r2) of 0.997, 0.992, and 0.995, respectively. Using three different samples and IMPA spiked into the quenched agar matrix at three levels (10, 100, and 1000 μg/mL), analysis accuracy was reflected by average spike recoveries of 76, 79, and 84%, respectively.